Passenger vehicles typically include a number of structural components, such as a rocker or rocker panel (hereinafter referred to as “rocker panel”). A rocker panel is a longitudinally extending side structural component normally designed to integrally join to a lower body structure of a vehicle, and to fit below the base of a door opening and between wheel wells. A rocker panel is intended to provide strength and stiffness to a vehicle body, and forms part of integral Body in White (“BIW”) structural components with respect to load transfer and vehicle crash safety performance.
A rocker panel may include an inner rocker panel to be placed proximal to a vehicle interior, and an outer rocker panel welded, secured or coupled to the inner rocker panel for placement distal to the vehicle interior. An inner rocker panel may include an elongated metal beam having a generally “U”-shaped cross-sectional profile, and can be produced with a high strength steel sheet, such as that having the grade DP590T to DP980T, cold formed into a desired profile. To reduce vehicle weight while avoiding significant loss of strength and stiffness, it may be desirable to utilize steel materials of higher strength, such as those having an ultimate tensile strength as high as 1300 MPa to 1900 MPa, in the production of an inner rocker panel. With increased tensile strength, however, the steel materials may suffer disadvantages in that material flatness, formability and joint strength may be reduced.
As an alternative or supplemental strategy, it may be desirable to produce an inner rocker panel with a high strength steel of reduced gage thickness, and introduce local reinforcements where greater strength, stiffness and Noise, vibration and harshness (“NVH”) performance may be required. Various locally reinforced metal blanks, such as tailor welded blanks, tailor rolled blanks and patch type tailor welded blanks, have been utilized in the past to prepare various locally reinforced vehicle structural components. For example, a tailor welded blank includes a number of metal pieces of different thicknesses or grades which are welded together in an edge-to-edge arrangement. A patch type tailor welded blank is a variant of the tailor welded blank, and includes a reinforcing patch overlapping a portion of a parent blank.
While a tailor welded blank may provide for advantages in significant overall weight reduction, a patch type tailor welded blank or patch type reinforcement may provide for improved overall material integration, and thus improved load transfer and distribution of stresses. Even with patch type reinforcement, however, increasing metal strength grades remains to provide challenges with respect to formability and bendability, especially in forming structural components requiring heavily formed profiles or bend angles.
U.S. Pat. No. 3,209,432 to Cape describes a side rail component where two metal strips are shown as overlapping and generally integrally joined together by for example by spot/pressure welding and/or bonding prior to bending. It has been appreciated that such joining solutions of Cape may not be practical, and become increasingly unworkable for higher bend angles and material strength for configurations, bending processes and applications such as a vehicle rocker panel. For instance, during bending, substantial internal stresses may develop within each material layer, planar and transversal throughout the deformed portion of the bend line. It has been appreciated that each layer has a natural neutral axis as a function of the layers bend radius, and are subject to the strain differential created between inner and outer strips, as a result of the different bend line radii and arc lengths. Severe residual stresses can remain after bending, compromising the structural and dimensional integrity of the structure.
High strength sheet metal rocker panels are known to be produced by cold forming processes, such as stamping, roll forming and bending. Furthermore, patch type reinforcements are known to be used in hot form stamping processes (see for example U.S. Publication No. 2014/0193659 to Lanzerath), where high ductility in a hot state allows for improved formability. The increased ductility of a patch blank allows for increased strain capacity when drawn or bent to shape without significant damage to the material properties. However, significant material thinning can be anticipated, predominantly in the in outer sheet relative to the bend line and good potential for damage within surrounding sheet securement welds/integration. It has been appreciated to be also difficult and expensive to achieve material properties at full potential and distortion control due to non-uniform heating and quenching in the post form heat treating process. The process is relatively complex and high cost.